Semiconductor device having improved thermal properties

ABSTRACT

A semiconductor device includes: a first heat spreader; a second heat spreader separated from the first heat spreader; a first semiconductor element on the first heat spreader and having a back face jointed to the first heat spreader; a second semiconductor element on the second heat spreader and having a back face jointed to the second heat spreader; a resin coating the first and second heat spreaders and the first and second semiconductor elements; and a reinforcing member provided across a region between the first and second heat spreaders in the resin, and having rigidity higher than rigidity of the resin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device used in an inverter to control a motor used in automobiles or electric trains, or in a converter for electric generation or regeneration.

2. Background Art

A semiconductor device wherein a semiconductor element is mounted on a heat spreader, and the heat spreader and the semiconductor element are sealed with a resin has been used (for example, refer to Japanese Patent Application Laid-Open No. 2004-165281).

SUMMARY OF THE INVENTION

In a semiconductor device wherein each of semiconductor elements is mounted on two heat spreaders separated from each other, a resin is present in the region between the two heat spreaders. Due to the difference in the linear expansion coefficients between the resin and the heat spreader, when heat is generated and temperature change occurs during the use, thermal stress occurs. For this reason, when excessive hot-cold cycles are applied, a warpage occurs from the region between the two heat spreaders. Further, there has been a problem wherein abrasion develops between the resin and internal members such as the heat spreader or lead frames, and reliability is affected.

In view of the above-described problems, an object of the present invention is to provide a semiconductor device which can inhibit the warpage by thermal stress and improve the reliability.

According to the present invention, a semiconductor device includes: a first heat spreader; a second heat spreader separated from the first heat spreader; a first semiconductor element on the first heat spreader and having a back face jointed to the first heat spreader; a second semiconductor element on the second heat spreader and having a back face jointed to the second heat spreader; a resin coating the first and second heat spreaders and the first and second semiconductor elements; and a reinforcing member provided across a region between the first and second heat spreaders in the resin, and having rigidity higher than rigidity of the resin.

The present invention makes it possible to inhibit the warpage by thermal stress and improve the reliability.

Other and further objects, features and advantages of the invention will appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a semiconductor device according to the first embodiment of the present invention.

FIG. 2 is a perspective top view showing the interior of the semiconductor device according to the first embodiment of the present invention.

FIG. 3 is a perspective top view showing the interior of the semiconductor device (from which reinforcing members are omitted) according to the first embodiment of the present invention.

FIG. 4 is a sectional view taken along the line I to II in FIG. 2.

FIG. 5 is a sectional view taken along the line III-IV in FIG. 3.

FIG. 6 is a perspective top view showing the interior of a semiconductor device in a modification example (from which reinforcing members are omitted) according to the first embodiment of the present invention.

FIG. 7 is a sectional view showing a semiconductor device according to the second embodiment of the present invention.

FIG. 8 is a perspective top view showing the interior of a semiconductor device according to the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A semiconductor device according to the embodiments of the present invention will be described with reference to the drawings. The same components will be denoted by the same symbols, and the repeated description thereof may be omitted.

First Embodiment

FIG. 1 is a circuit diagram showing a semiconductor device according to the first embodiment of the present invention. Six pairs of transistor elements 1 a to 1 f and diodes 2 a to 2 f constitute a three-phase half-bridge circuit. An electric power from a power source is supplied to the load via U, V, and W terminals. The transistor elements 1 a to 1 f are insulated gate bipolar transistors (IGBT) which conduct electric currents supplied from the power source for only required times. The diodes 2 a to 2 f reflux electric current when the transistor elements 1 a to 1 f become the blocking state from the conducting state.

FIG. 2 is a perspective top view showing the interior of the semiconductor device according to the first embodiment of the present invention. FIG. 3 is a perspective top view showing the interior of the semiconductor device (from which reinforcing members are omitted) according to the first embodiment of the present invention. FIG. 4 is a sectional view taken along the line I to II in FIG. 2.

Heat spreaders 3 a to 3 c and heat spreaders 3 d to 3 f are separately arranged on the left and the right. The heat spreaders 3 a to 3 f are separated from each other. The transistor elements 1 a to 1 c and the diodes 2 a to 2 c are respectively mounted on the heat spreaders 3 a to 3 c, and the back faces thereof are separately joined to the heat spreaders 3 a to 3 c with a solder 4. The transistor elements 1 d to 1 f and the diodes 2 d to 2 f are respectively mounted on the heat spreaders 3 d to 3 f, and the back faces thereof are separately joined to the heat spreaders 3 d to 3 f with the solder 4.

Wiring members 5 a to 5 c separated from each other are respectively joined to the upper faces of the transistor elements 1 a to 1 c and the diodes 2 a to 2 c with the solder 4. A wiring member 5 d is joined on the upper faces of the transistor elements 1 d to 1 f and the diodes 2 d to 2 f with the solder 4 in common. In place of the solder 4, a conductive adhesive or the like can also be used. The wiring members 5 a to 5 c are respectively joined to the peripheral portions on the upper faces of the heat spreaders 3 d to 3 f. Wiring members 5 e to 5 g separated from each other are respectively joined to the peripheral portions on the upper faces of the heat spreaders 3 a to 3 c.

Signal wirings 6 a to 6 c are respectively connected by wires to the control terminals of the transistor elements 1 a to 1 c. Signal wirings 6 d to 6 f are respectively connected by wires to the control terminals of the transistor elements 1 d to 1 f. For insulation from the exterior, an insulating layer 7 is provided on the back face of the heat spreaders 3 d to 3 f. These heat spreaders 3 a to 3 f, the transistor elements 1 a to 1 f, the diodes 2 a to 2 f, parts of the wiring members 5 a to 5 g, parts of the signal wirings 6 a to 6 f, and the upper faces and the side faces of the insulating layer 7 are coated with a molding resin 8.

The wiring members 5 a to 5 g assume receiving and sending the electric power from and to the exterior of the device. The wiring members 5 a to 5 g and the signal wirings 6 a to 6 f are formed in the state wherein, for example, the identical metal plates are punched or etched to be integrally connected at the outer frame. Parts of them are coated with the molding resin 8 to mechanically hold them, and the outer frame is removed to divide the wiring members 5 a to 5 g and the signal wirings 6 a to 6 f. Thereby, since a large number of wiring members 5 a to 5 g and signal wirings 6 a to 6 f can be assembled at once, the productivity is improved, and the industrial value is elevated.

In the present embodiment, a reinforcing member 9 having the rigidity higher than the rigidity of the molding resin 8 is provided across the region between heat spreaders 3 a to 3 f in the molding resin 8. The reinforcing member 9 is provided above the transistor elements 1 a to 1 f and the diodes 2 a to 2 f without contacting to the transistor elements 1 a to 1 f and the diodes 2 a to 2 f.

The reinforcing member 9 is, for example, a metallic plate member. If the reinforcing member 9 is a metallic member, it has a sufficiently higher Young's modulus than the molding resin 8. Therefore, the reinforcing effect can be improved. In addition, when the reinforcing member 9 is fabricated with organic materials reinforced like fiber-reinforced plastics, ceramic materials, or the like, it is preferred for weight saving. Further, the reinforcing member 9 is not limited to a plate shape, but can have an L- or U-shape so as to inhibit bending.

By reinforcing the region between the heat spreaders 3 a to 3 f with the reinforcing member 9, the warpage caused by thermal stress can be inhibited in such a region. As a result, breakage can be prevented and reliability can be improved.

In addition, the transistor elements 1 a to 1 f, the diodes 2 a to 2 f, the heat spreaders 3 a to 3 f, the wiring members 5 a to 5 g, and the signal wirings 6 a to 6 f constitute a three-phase half bridge circuit required in the inverter circuit for controlling the load of the motor or the like. As described above, in the case where a three-phase half bridge circuit is constituted with one semiconductor device, the package size is enlarged, and the problem of warpage becomes significant. However, since warpage can be inhibited by the constitution of the present embodiment, the reliability can be improved.

Further, the wiring members 5 a to 5 c intersect the region between the heat spreaders 3 a to 3 c and the heat spreaders 3 d to 3 f to connect the upper faces of the transistor elements 1 a to 1 c and the heat spreaders 3 d to 3 f, respectively. With functioning as electric circuits, the wiring members 5 a to 5 c can reinforce the relevant region. Therefore, without increasing the number of parts, the warpage by thermal stress can be inhibited. As a result, the reliability can be improved without impairing productivity.

FIG. 5 is a sectional view taken along the line III-IV in FIG. 3. Even if the wiring members 5 a to 5 c have a flat structure, reinforcing effects can be obtained due to the rigidity of the metal. However, by providing a U-shaped indent 10 in parts of the wiring members 5 a to 5 c in the direction from the upper face to the back face, the rigidity in the thickness direction can be improved. If the depth of the indent 10 is about 1.5 times the thickness of the wiring members 5 a to 5 c, processing can be performed, and a sufficient reinforcing effect can be obtained. Further, the indent 10 can be provided in the direction from the back face to the upper face of the wiring members 5 a to 5 c. The shape of the indent 10 is not required to be U-shaped, but can be triangular or semicircular.

FIG. 6 is a perspective top view showing the interior of a semiconductor device in a modification example (from which reinforcing members are omitted) according to the first embodiment of the present invention. The transistor elements 1 a to 1 c and the diodes 2 a to 2 c are mounted on one heat spreader 3 g in parallel and the back faces thereof are commonly joined to the heat spreader 3 a with the solder 4. Thereby, the left side of the device is supported by the heat spreader 3 g having a high rigidity. A wiring member 5 h is joined to the peripheral portion of the upper face of the heat spreader 3 g.

As described above, the heat spreaders 3 a to 3 c having the same potential are gathered to one heat spreader 3 g, and the warpage of the package in the longitudinal direction of the heat spreader 3 g can be reduced. In addition, the number of the parts can be reduced, and the assembly can be simplified. Furthermore, it is preferable that the longitudinal direction of the heat spreader 3 g is parallel to the terminal takeout face of the package because wiring is easy. However, the vertical direction to the terminal takeout face is also feasible.

Second Embodiment

FIG. 7 is a sectional view showing a semiconductor device according to the second embodiment of the present invention. Since insulation between elements is ensured under the insulating layer 7, a copper foil 11 is provided under the insulating layer 7 across a plurality of heat spreaders 3 a to 3 f. The copper foil 11 is thicker than the insulating layer 7, and intersects the region between the heat spreaders 3 a to 3 f. By reinforcing the region between the heat spreaders 3 a and 3 f with the thickened copper foil 11, the warpage caused by thermal stress in the region can be inhibited. As a result, breakage can be prevented and reliability can be improved. In addition, the copper foil 11 can also be used as the adhesion of the package and the cooler.

Third Embodiment

FIG. 8 is a perspective top view showing the interior of a semiconductor device according to the third embodiment of the present invention. The heat spreader 3 g has a concave portion 12 facing the heat spreaders 3 d to 3 f. The heat spreaders 3 d to 3 f have extended portion 13 entering into the concave portion 12. Thereby, the region between the heat spreader 3 g and the heat spreaders 3 d to 3 f are reinforced, and warpage caused by thermal stress in the region can be inhibited. As a result, breakage can be prevented, and reliability can be improved. In addition, although the shape of the extended portion 13 is preferably rectangular along the shape of the semiconductor element, it can be curved like an S-line, or can be triangular.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

The entire disclosure of a Japanese Patent Application No. 2012-103244, filed on Apr. 27, 2012 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety. 

What is claimed is:
 1. A semiconductor device comprising: a first heat spreader; a second heat spreader separated from the first heat spreader; a first semiconductor element on the first heat spreader and having a back face jointed to the first heat spreader; a second semiconductor element on the second heat spreader and having a back face jointed to the second heat spreader; a resin coating the first and second heat spreaders and the first and second semiconductor elements; and a reinforcing member provided across a region between the first and second heat spreaders in the resin, the reinforcing member making direct contact only with the resin and having rigidity higher than rigidity of the resin.
 2. The semiconductor device according to claim 1, wherein the reinforcing member is provided above the first and second semiconductor elements without contacting to the first and second semiconductor elements.
 3. The semiconductor device according to claim 1, further comprising a wiring member connecting an upper face of the first semiconductor element to the second heat spreader and having an indent.
 4. The semiconductor device according to claim 1, wherein the first semiconductor element includes a plurality of semiconductor elements, and back faces of the plurality of semiconductor elements are commonly joined to the first heat spreader.
 5. The semiconductor device according to claim 1, wherein the first and second heat spreaders and the first and second semiconductor elements constitute a three-phase half-bridge circuit. 